Gearboxes typically have shifting devices by means of which one of several selectable gear ratios can be selected, and thereby a specific rotational-speed and torque gear ratio can be set. With motor vehicle transmissions, a shifting device typically combines an inner and an outer gearshift, wherein the inner gearshift, which is the subject matter of the present invention, comprises components lying within a transmission housing, such as a control shaft, shift rails and synchronization components for selecting the respective gear ratio. In the field of modern motor vehicles, the elements of the inner shifting device are increasingly directly electronically controlled and actuated, such that mechanical components of an outer shifting device can largely be omitted. In these cases, the shifting movements of the components of the inner shifting device are caused directly by electronic actuators disposed within the transmission housing.
From the document DE 600 01 023 T2 a shifting device of a gearbox is known, in which sliding sleeves can be moved axially by means of actuating means in the form of shifting forks assigned thereto, in order to purposefully select an associated gear ratio of the gearbox by the respective axial movement. It is widely known that the sliding sleeves are each disposed in a rotationally fixed and axially movable manner on a transmission shaft that additionally supports an idler gear at least on one side adjacent to the respective sliding sleeve. Here, these idler gears can rotate freely on the transmission shaft and are in permanent engagement with pinions of a further transmission shaft disposed as a countershaft or as a parallel input or output shaft. The selectable gear ratios of the gearbox are defined according to the tooth ratios of the respectively meshing gears. With axial movement of the respective sliding sleeve from a neutral position in the direction of the respective idler gear into a shifting position, upon reaching the shifting position, this idler gear is coupled by the sliding sleeve to the transmission shaft, and thus, the rotational speeds and torques are transmitted from one transmission shaft to the other transmission shaft at the respective defined gear ratio.
In the document DE 600 01 023 T2, the shifting forks of the individual sliding sleeves are guided in an axially movable manner on a common control shaft, which can be rotated as desired via a pinion disposed on an end side by means of an electric actuating element. Furthermore, a cylinder is placed on the control shaft in a fixed connection thereto that on an outer diameter has a groove running in a curve in an axial direction. Furthermore, a bushing placed on the cylinder has a pin stamped on the inner diameter thereof that engages in the groove of the cylinder, and upon rotation of the control shaft performs an axial movement on the cylinder, corresponding to the course of the groove of the cylinder. Furthermore, the bushing, on the outer diameter thereof, has shifting fingers which, depending on the angular position of the bushing, contact one of the shifting forks and correspondingly transmit the axial movement of the bushing to the respective fork. In order to set the respective angular position of the bushing, the bushing is engaged, via a gearing, with an intermediate shaft that in turn is in contact, via a gear, with the control shaft.
Upon rotation of the control shaft by means of the electric actuating element, the bushing is moved in the axial direction according to the rotation of the cylinder, and thereby guides one of the shifting forks along with the bushing, such that ultimately movement of the respective sliding sleeve is initiated, and thus the selection of an associated gear ratio is initiated. Corresponding to the gear ratio between the control shaft and the intermediate shaft, the intermediate shaft in addition rotates the bushing during rotation of the control shaft with respect thereto, so that the shifting fingers come into successive contact with the individual shifting forks according to the shifting sequence of the manual gearbox. Thus, upon actuation of the electric actuating element, a consecutive upshift, or downshift is possible.